1. Field of the Invention The present invention relates to a vehicular lamp unit that uses a semiconductor light-emitting element such as an LED as a light source.
2. Background Art
There are an increasing number of cases in recent years where a vehicular lamp that includes a headlamp is mounted with an LED (semiconductor light-emitting element) that is compact, lightweight, and has excellent light-emitting efficiency. An LED chip used as the light source normally has a light-emitting surface with a generally oblong shape, and the LED chip is disposed such that a side end of the light-emitting surface coincides with a focal line of a reflective surface formed from a parabolic cylindrical curved surface or the like (see Patent Document 1 for an example).
Depending on driving conditions, two light distribution patterns are required of a vehicular lamp: a light distribution pattern in which diffused light is distributed in front of the vehicle and localized condensed light is weakened; and a light distribution pattern in which less diffused light is distributed in front of the vehicle and condensed light to localized portions is strengthened so that a boundary between an illuminated portion and a non-illuminated portion is clearly apparent. A particularly effective light distribution pattern during rainy weather or the like is one that reduces luminance toward the front side of the vehicle (on top of the road surface). The difference between the above two light distribution patterns is the vertical-direction spread and the intensity of condensed light in the light distribution patterns.
[Patent Document 1]
Japanese Patent Application Publication No. JP-A-2003-31011, pages 3 to 6, FIG. 1.